Ok I adjusted the accelerator pump linkage and from start the bog is gone.It's a vacuum advance... Not sure about curve or how to map it. Carb has vacuum secondaries.
Is it worth picking up a smaller power valve? They are only $8 and are QUOTE]
To map the distributor curve:
You mush have an advance timing light with a dial on the back.
Start the engine and let it idle. Connect the timing light and a tune up tachometer (engine analyzer) to the engine. Record the RPM and how many degrees advanced you are.
Then bump it up to the next "level" (I suggest going by every 250 RPM). So then use 1000 RPM and then check the timing and record it.
Keep increasing RPM 250 until you get to 3500 or 4000.
You can check this with and then without vacuum advance to see the difference.
Now for the power valve. Yes, I think you should think about changing it. Here's how to determine what to do:
POWER ENRICHMENT SYSTEM
The power enrichment system supplies additional fuel to the
main system during heavy load or full power situations. Holley
carburetors utilize a vacuum operated power enrichment system
and a selection of power valves is available to time this systems
operation to your specific needs. Each Holley power
valve is stamped with a number to indicate the vacuum opening
point. For example, the number 65 indicates that the power
valve will open when the engine vacuum drops to 6.5" or
below. An accurate vacuum gauge, such as Holley P/N
26-501, should be used when determining the correct power
valve to use. A competition or race engine which has a long
duration high overlap camshaft will have low manifold vacuum
at idle speeds. If the vehicle has a manual transmission, take
the vacuum reading with the engine thoroughly warmed up and
at idle. If the vehicle is equipped with an automatic transmission,
take the vacuum reading with the engine thoroughly
warmed up and idling in gear. In either case, the power valve
selected should be 1/2 the intake manifold vacuum reading
taken. EXAMPLE: 13 Hg vacuum reading divided by 2 = 6.5
power valve. If your reading divided by 2 lands on an even
number you should select the next lowest power valve. EXAMPLE:
8 Hg vacuum reading divided by 2 = 4 power valve.
Since there is no #4 power valve you should use a 3.5.
Most of the popular Holley Street Legal and Street
Performance carburetors incorporate a power valve blow-out
protection system. A special check valve is located in the throttle
body expressly for this purpose. This check valve is
designed to be normally open but will quickly seat to close off
the internal vacuum passage when a backfire occurs. Once
closed, the check valve interrupts the pressure wave caused by
the backfire, thus protecting the power valve.
If you have a carburetor older than 1992 (or you have experienced
an extreme backfire) and expect a blown power valve,
use this simple test. TEST: At idle turn your idle mixture screws
(found on the side of the metering block) all the way in. If your
engine dies the power valve is not blown.
THE TRUTH ABOUT POWER
VALVES USED WITH HOLLEY
CARBURETORS
There still seems to be a lot of misconception about
Holley carburetors blowing power valves. Nothing
could be further from the truth. Holley performance
carburetors built since 1992 have utilized a power
valve check system that effectively eliminated this
infrequent problem. Consisting of a spring, brass
seat and check ball, the check ball system is 100%
effective protecting the power valve diaphragm
from damage due to engine backfire.
The power valve check ball is designed to be
normally open but quickly seals to close off the
internal vacuum passage when a backfire occurs.
Once closed, the check valve interrupts the pressure
wave generated by the backfire, thus protecting the
power valve diaphragm. There is no way that the
power valves diaphragm
